The present invention relates to a new and improved construction of a gearing arrangement for a grinding apparatus, especially for a bowl-type grinder or grinding mill.
Generally speaking, the gearing arrangement of the present development is of the type comprising a lower housing portion and an upper housing portion attached to the lower housing portion. Mounted upon the upper housing portion by means of an axial bearing and a radial bearing is a mounting or support plate for a grinding bowl or receptacle, this mounting plate having a substantially vertical axis of rotation. Additionally, there is provided angular gearing containing a substantially horizontal drive shaft and a power take-off shaft arranged essentially coaxially with respect to the mounting or support plate. There is also provided planetary gearing containing a sun gear which is coupled with the power take-off shaft of the angular gearing, at least one planetary gear, a planetary gear support which is coupled with the mounting or support plate, and a substantially ring-shaped outer central gear which is affixed to the lower housing portion.
According to a known construction of gearing arrangement of this character for a bowl-type grinding mill or grinding apparatus, as disclosed for instance in German patent publication No. 2,716,025, published Oct. 19, 1978, the lower housing portion possesses a cylindrical supporting wall in which there is mounted the horizontal drive shaft of angular gearing and directly thereabove there is secured the ring-shaped outer central gear of the planetary gearing. Accordingly, there are also housed above the angular gearing, within the lower housing portion, all of the remaining gears of the planetary gearing. The lower housing portion possesses a flange above the planetary gearing. This flange is bolted to a corresponding flange of the upper housing portion. This upper housing portion likewise has a cylindrical wall which encloses the rotatable support or mounting plate as well as its axial and radial bearings. The planetary gear support which is arranged in the lower housing portion is suspended in a pendulum-like fashion at the mounting plate by means of an axially arranged traction rod and is only centered in that the planetary gears mounted therein mesh with the outer central gear. The sun gear of the planetary gearing is supported in axial direction upon the power take-off shaft of the angular gearing by means of crowned surfaces and is coupled by a double-tooth clutch or coupling with such power take-off shaft. Centering of the sun gear is likewise accomplished by the planetary gears which mesh therewith.
In this way there is ensured that the sun gear is accommodated to the position of the planetary gears which, in turn, accommodate themselves to the position of the outer central gear. However, the strived for objective that the tooth flanks of all gears uniformly support the loads is not attainable with the operating conditions which arise with a bowl-type grinding mill or grinding apparatus. In particular, during operation there additionally act upon the axial bearing, apart from the extremely large weight of the mounting or support plate and the grinding bowl, the weight of a roller framework together with the rolls which roll upon the grinding bowl. This weight is also frequently intensified in that, the roller framework is downwardly biased or loaded by means of, for instance, a hydraulic device, in order to increase the roller pressure. Therefore, there can act upon the axial bearing of a bowl-type grinding mill of the aforementioned type, axial forces in the order of magnitude of 400 tons which, with the heretofore known constructions of gearing arrangements or transmissions for bowl-type grinding apparatus, can cause bending moments in the upper housing portion which are transmitted by means of the lower housing portion to the ring-shaped outer central gear. These transmitted forces in any event then tend to deform the central gear if the supporting housing walls are not designed to be extraordinarily strong which, accordingly, constitutes an extremely expensive construction. Therefore, there cannot be ensured that the gears of the planetary gearing will uniformly carry the loads over their entire tooth width in the presence of all operating conditions which arise.